In 1999, the NLM Office of High Performance Computing and Communications awarded multiple contracts for the formation of a software development consortium to create and develop an application programmer interface (API) and first implementation of a segmentation and registration toolkit, subsequently named the Insight Toolkit (ITK). The original awards included six contractors: GE Global Research, Insightful, Inc., Kitware, Inc., the University of North Carolina at Chapel Hill, the University of Pennsylvania, and the University of Tennessee. The six contractors were partnered with five subcontractors: Harvard University Medical School, the University of Pennsylvania, the University of Pittsburgh, Columbia University, and the University of Utah. The period of performance for the original ITK awards began in 1999 and ended in 2003. The resulting system was originally intended for computer-assisted exploration of the National Library of Medicine (NLM) Visible Human (VHP) data sets. The final deliverable for this group was an open-source software library concentrating on segmentation and registration algorithms, directly inserted into the public domain that now helps support research worldwide in image analysis and in other domains. Open-source initiatives such as ITK help to lower the barriers to entry in complex research fields by providing the foundations of the software infrastructure necessary to conduct advanced investigations. Revising ITK is considered a contribution to the nation's infrastructure through software. Careful thought has been placed on the cultivation and maintenance of this software, assuring developers that the software will remain supported with new releases, bug fixes, and continuing growth. The Insight Toolkit (ITK) is currently available with the release, ITK version 3.16, announced in September 2009 (see the URL: http://www.itk.org). Despite continued support through systems technology contracts, NLM wishes to revisit the underlying design and software architecture for ITK at this time. The initial design meeting for ITK was held in early November 1999, and while the design decisions for this software were targeted for the anticipated technology of 2004, those decisions are now showing their age.